Preheat oven to 375°F. Set a rack in the center position.
Blind-bake the crust: line with parchment, fill with pie weights, and bake 12 minutes. Remove weights and bake 5 minutes more. Cool slightly.
Cook the bacon in a skillet over medium heat until crisp, 6–8 minutes. Transfer to a paper towel–lined plate.
Séar the onion in 1 tbsp butter and a spoonful of bacon fat until translucent, 3–4 minutes. Let cool.
Whisk eggs, cream, and milk in a bowl. Season with salt, pepper, and nutmeg until smooth and frothy.
Scatter half the cheese in the crust. Top with bacon and onion. Add remaining cheese evenly.
Pour the custard over the filling. Place the pie on a rimmed sheet to catch any drips.
Bake until the center is just set and slightly wobbly, 35–40 minutes. Rest 15 minutes before slicing.
Finish with chives, slice into wedges, and serve warm or at room temperature.
Notes
Variation: Swap Gruyère with Swiss or add a pinch of smoked paprika for extra depth. Make-ahead: Bake, cool, and refrigerate up to 3 days; reheat at 325°F until warm.This recipe is an original creation inspired by classic Easy Quiche Lorraine Recipe flavors. All ingredient ratios and instructions are independently developed.